A number of structurally unique C.sub.11 N.sub.5 marine metabolites containing guanidine and either brominated or nonbrominated pyrrole moieties have been isolated from various sponges..sup.1 Among these are the tricyclic natural products hymenin (1),.sup.2 stevensine (2),.sup.3,4 hymenialdisine (3),.sup.4-8 and debromohymenialdisine (4)..sup.4-9 This group of natural products share in common a fused bicyclic pyrrolo[2,3-c]azepin-8-one ring system that bears either a 2-aminoimidazole (AI) or glycocyamidine appendage. Their structures were elucidated primarily from spectral studies in comparison with biogenetically and structurally related sponge metabolites. The X-ray crystal structure of 3 has been reported by two research groups..sup.5,6 Hymenialdisine (3) is the only metabolite among the C.sub.11 N.sub.5 and dimerically related natural products that contains a monobromo pyrrole moiety in which the bromine atom is situated in the a position..sup.10 This invention describes a synthesis of this family of natural products consisting of 1-4.